Transistors are key components of modern integrated circuits. To satisfy the requirements of increasingly faster switching speed, the drive currents of transistors need to be increasingly higher. At the same time, the gate lengths of transistors are constantly being scaled down. Scaling down the gate lengths leads to undesirable effects known as “short-channel effects,” with which the control of current flow by the gates is compromised. Among the short-channel effects are the drain-induced barrier lowering (DIBL) and the degradation of sub-threshold slope, both of which result in the degradation in the performance of transistors.
The use of multi-gate transistor architecture may help the relief of short-channel effects by improving electrostatic control of the gate on the channel. Fin field-effect transistors (FinFET) were thus developed. To further increase the control of the channels, and to reduce the short-channel effects, transistors having vertical gate-all-around structures were also developed, wherein the respective transistors are also referred to as Vertical Gate All Around (VGAA) transistors. In a VGAA transistor, a gate dielectric and a gate electrode fully encircle a channel region. This configuration delivers a good control of the channel, and the short-channel effects are reduced.
The connection to the source and drain regions of the VGAA transistors is through contact plugs and metal lines. Contact plugs are formed to electrically connect to the top source/drain regions, the bottom source/drain regions, and the gates of the VGAA transistors. Metal lines are used to interconnect the contact plugs. When a local interconnector is needed to electrically interconnect the top source/drain regions of neighboring VGAA transistors, the local interconnector includes the contact plugs and the metal line interconnecting the contact plugs.